The SIP is a very robust protocol that has become ubiquitous in the telecommunication industry. SIP is the core protocol for most voice and video communication products that are being shipped today. The proliferation of SIP has lead to a variety of SIP based standards that allow for conformance between communication equipment provided by different vendors. However, the existing SIP standards fall short in dealing with all types of conditions that are prevalent in SIP communication networks.
For example, the SIP standard disclosed in RFC3261 and the Best Current Practices (BCP) document disclosed in RFC5407 describe how to deal with glare conditions for communication devices that are engaged in the same SIP dialog. A glare condition is where a device, such as a telephone, has sent a first request and receives a second request before receiving an acknowledgment to the first request. For example, a glare condition in the same dialog results when a telephone sends a hold command to another telephone on the same call while receiving a hold command simultaneously from the other telephone. The result can be a prolonged waiting period before either request is processed.
The existing SIP RFCs describe how to handle glare conditions for in-dialog SIP requests (e.g., where a SIP communication session has been established between the devices). However, the existing SIP RFCs do not describe how to deal with glare conditions that occur as a result of out-of-dialog operations. This may result in unexpected behavior of products and may lead to interoperability issues.